1. Field of the Invention
The present invention generally relates to switching regulators, and more particularly to a switching regulator that can suppress an inrush current.
2. Description of Related Art
A switching regulator is connected to a power supply for receiving an input voltage and outputting an output voltage. The switching regulator typically includes an electrical switch, such as a metal-oxide semiconductor field-effect transistor (MOSFET) or a bipolar junction transistor (BJT), a capacitor, and a controller. The electrical switch is used for switchably applying the input voltage to the capacitor, and the capacitor is used for filtering the input voltage to form the output voltage. The output voltage is fed back to the controller. The controller adjusts a time span during which the electrical switch is switched on.
When the switching regulator is switched to the on state, an inrush current may be generated abruptly. The inrush current is extraordinarily greater than a normal input current. Referring to FIG. 5, for instance, the normal input current is lower than 50 A, whereas the inrush current rises to 100 A. Such a great inrush current may destroy the switching regulator. Therefore, it is necessary to suppress the inrush current, so as to protect the switching regulator from damage.
Referring to FIG. 6, a conventional switching regulator 900 is shown. The switching regulator 900 includes a rectifier D1, a filter C1, and a thermistor R1. The filter C1 is an electrolytic capacitor. The thermistor R1 is a resistor whose resistor varies with temperature. That is, the resistance of the thermistor R1 increases as the temperature decreases. An end of the thermistor R1 is electrically connected to a positive output end of the rectifier D1, and the other end of the thermistor R1 is electrically connected to a positive pole of the filter C1. A negative pole of the filter C1 is electrically connected to a negative output end of the rectifier D1.
When the switching regulator 900 is powered on, the rectifier D1 converts an alternating current to a direct current, and charges the filter C1 with the direct current via the thermistor R1. The resistor R1 can suppress the inrush current because of its characteristic.
However, the thermistor R1 does not cool down rapidly after the switching regulator 900 is powered off, the resistance of the thermistor R1 will not increase rapidly. Thus, if the switching regulator is promptly powered on, the thermistor R1 cannot suppress the inrush current.
Therefore, a new switching regulator is needed in the industry to address the aforementioned deficiencies and inadequacies.